MORPHOLOGY AND BIOLOGY OF BACTERIA. 27 



terest. The ability of various bacteria to effect chemic 

 decomposition may, from the present state of knowledge, 

 be considered as extremely varied. The most profound re- 

 ductions, and the most far-reaching oxidations, the forma- 

 tion of most complex combinations and their disintegration 

 into atoms, are effected by bacteria. From nitrates are 

 formed nitrites, free nitrogen, and ammonia ; on the other 

 hand, bacteria in the earth are capable of forming nitrates 

 from nitrogen and ammonia. The bacteria of earth which 

 are responsible for the process last named the so-called 

 nitrification-process are of great biologic interest. They 

 oxidize the ammonia the final product of the de- 

 composition of nitrogenous substances into nitrites, and 

 these further into nitrates, which then enter into the forma- 

 tion of new plants. Winogradsky recognized two varieties 

 the nitrosobacteria (niirosococcus and nitrosomonas), 

 which oxidize ammonia into nitrites, but not further ; and the 

 nitrobacteria, which are incapable of acting upon the am- 

 monia, but, on the other hand, convert the nitrites into 

 nitrates. Both species are characterized by the remarkable 

 fact that they grow only in culture-media that contain no 

 trace of organic carbon-compounds that is, they are 

 capable of obtaining the carbon they require from the car- 

 bon dioxid of the atmosphere, without the aid of chloro- 

 phyl. 



Under appropriate nutritive conditions bacteria de- 

 velop hydrogen sulphid from all sulphur-containing com- 

 pounds. The so-called sulphur-bacteria (beggiatoa, thio- 

 thrix) require a supply of hydrogen sulphid, extracting the 

 sulphur and storing it up in their protoplasm in the form of 

 bright granules. With deficiency of nutritive material the 

 sulphur-granules are oxidized into sulphuric acid. 



Urea is decomposed into carbon dioxid and ammonia. 

 There is scarcely an organic combination from which these 

 gases and also free hydrogen may not finally be produced 

 through bacterial activity. 



Of especial significance is the bacterial decomposition of 

 substances that serve for the nutrition and for the construc- 

 tion of the body. Starch is dextrinized, saccharified, even 

 subjected to mucoid transformation. Sugar undergoes vari- 

 ous forms of fermentation in consequence of bacterial activ- 

 ity ; alcohol, carbon dioxid, acetic acid, lactic acid, butyric 

 acid, succinic acid, and others, have been demonstrated 



